In the past, there have been used an optical coherent tomography (OCT) apparatus (see, for example, Japanese Application Publication No. 2010-14501) and an optical frequency domain imaging (OFDI) apparatus utilizing wavelength sweep, which is an improved type of optical coherent tomography apparatus, for a result confirmation after operation at the time of treatment inside a blood vessel depending on a high functional catheter such as a stent and the like. Hereinafter, in the present specification, the optical coherent tomography (OCT) apparatus and the optical frequency domain imaging (OFDI) apparatus utilizing wavelength sweep will be generically referred to as “optical imaging apparatus for diagnosis”.
Specifically, these apparatus are utilized for specifying the position of a stent indwelled inside a body lumen (for example, inside a blood vessel) and the position of a biological tissue from an imaged tomographic image and for confirming an arrangement the stent takes with respect to the inner wall of the biological tissue.
Here, the stent is generally made of a metal through which the light cannot penetrate and is mesh-shaped. For this reason, the light illuminated from an optical probe is mostly reflected at the stent portion and does not reach the inner wall of the biological tissue, and so a situation arises in which only the light passing through aperture portions of the mesh will reach the inner wall. In consideration of such fact, in case of the tomographic image which is imaged by using an optical imaging apparatus for diagnosis, the stent and the inner wall will be respectively displayed as line segments which are discontinuous in the circumferential direction.
However, in a case in which the stent and the inner wall of the biological tissue are displayed as discontinuous line-segments, it becomes difficult for a user to comprehend the positional relationship between the stent and the inner wall, for example, to comprehend whether or not the stent is contacting the inner wall, whether or not the stent is spaced apart from the inner wall, or the like. Consequently, in an optical imaging apparatus for diagnosis, there is proposed a configuration in which a user can visually-comprehend the positional relationship between the stent and the inner wall, for example, by generating closed curves connecting the discontinuous line-segments (stent closed-curve and inner-wall closed-curve) and by displaying them by superimposing them on the tomographic image (for example, see U.S. Application Publication No. 2010/0094127.
However, in case of U.S. Application Publication No. 2010/0094127, there is not employed a construction in which noises in the region other than the stent and the inner wall are adequately removed, so that the generation of the closed curve will be carried out in a state in which noises of regions other than the stent and the inner wall are included. As a result, it can be assumed that the stent closed-curve and the inner-wall closed-curve, which are generated, will have shapes lacking in smoothness.
On the other hand, as mentioned above, because the stent is made of metal and has a certain amount of rigidity, there seldom happens a situation in which there occurs deformation accompanied by finely spaced concavity and convexity (precipitous concavity and convexity) in the circumferential direction with respect to the circular cross-sectional shape, and it is general that the stent becomes deformed to have a gradual curved-shape. In addition, also the inner wall of the biological tissue becomes deformed to have a gradual curved-shape in the circumferential direction with respect to the circular cross-sectional shape.
In consideration of such fact, it can be said, with regard to the closed curves of the stent and the inner wall of the biological tissue, that the fact of generating a more smooth shape precisely-reproduces the actual phenomenon inside the biological tissue (for example, blood vessel). Then, in order to reproduce such a closed curve, it becomes indispensable to exclude noises in the regions other than the stent and the inner wall as much as possible when generating the closed curve and to preliminarily-reduce the number of calculation points (number of stent candidate-points, number of inner-wall candidate-points) which are used for the generation of the closed curve.
However, when reducing the number of the calculation points too much, it is not possible to precisely-reproduce the cross-sectional shapes of the original stent and inner wall, and there is a possibility that there occurs a situation in which there are obtained shapes different from the cross-sectional shapes of the actual stent and inner wall. In consideration of such fact, it is desirable for the optical imaging apparatus for diagnosis to have a constitution in which the noises in the regions other than the stent and the inner wall are discriminated clearly from those of the stent and the inner wall, and in which the aforesaid noises can be removed reliably when generating the closed curves of the stent and the inner wall.